This invention relates to an induction system for a multi-cylinder engine having multiple carburetor barrels and more particularly to such an induction system that offers more balanced operation between the individual cylinders and improved combustion and efficiency throughout the entire engine range.
Recently it has been discovered that engine operation (both emission of unwanted exhaust gas constituents and fuel economy) can be improved, particularly at idle and low load operation by providing a sub-intake system through which a substantial portion of the induction charge flows to the combustion chambers under these operating conditions. By using a relatively small cross-sectional area induction system turbulence and, if desired, swirl may be generated in the combustion chamber at the time of ignition. As such, smoother and more efficient combustion results under these load conditions.
It has been proposed to control the flow through the sub-intake system by means of a main throttle valve and an auxiliary or sub-throttle valve which operate in sequence so as to cause substantially all of the idle and low load charge requirements to enter the combustion chambers through the sub-intake passage and to provide an increased flow through the main induction passage as the engine load increases. In connection with the adaptation of this concept to multiple chamber engines having multiple carburetor barrels, it has been proposed to provide only one of the carburetor barrels with a system for accommadating certain engine operating conditions. This one carburetor barrel can serve a plurality of chambers through the combined sub-intake passages, all of which are fed from this one carburetor barrel. An example of an application of this principal to a multiple cylinder engine may be found in the copending application of Hiromitsu Matsumoto, Ser. No. 838,353, entitled Control of Carburetor Supplied Induction System, filed Sept. 30, 1977 and assigned to the assignee of this application, such an arrangement being shown specifically in the embodiment of FIGS. 6-10 of that application. In that embodiment only one of the carburetor barrels is provided with a cold starting device in the form of a choke valve. This barrel serves other chambers in addition to the normally served by it during cold starting via an interconnected sub-intake system.
In accordance with an arrangement whereby multiple carburetors are used and one of these carburetors provides functions not provided by the other carburetors, uneven operation between the chambers may result under conditions other than that served by the single carburetor barrel. For instance, the use of a choke valve in only one carburetor barrel causes that carburetor barrel to have a greater flow resistance than the other carburetor barrels during unchoked operation. Thus, uneven mixture distribution and combustion may occur between the respective chambers.
It is, therefore, a principal object of this invention to provide an improved induction system for insuring even combustion between the respective chambers of a multi-chamber engine.
It is another object of the invention to provide an induction system for a multiple carburetor engine that improves efficiency without sacrificing even operation throughout the engine load and speed range.